RANS thermal modelling of a natural convection boundary layer at low Prandtl number

Abstract

The present work evaluates the performance of different RANS turbulence models in a natural convection boundary layer at three different Prandtl numbers: 0.71, 0.2 and 0.025. An assessment on the prediction of the boundary layer is presented in function of the wall fluxes, mean and turbulent flow fields. It is observed that the chosen turbulence model to close the momentum equation is relevant in order to capture the flow field at low Prandtl numbers. This is due to the strong interaction between the momentum and thermal fields in natural convection. From the thermal point of view, the analogy between the turbulent momentum and turbulent thermal diffusivities presents serious issues to correctly predict the flow field independently of the Prandtl number. Advanced models that employ algebraic or transport equations of the turbulent heat fluxes introduces the needed physics to correctly predict the natural convection boundary layer.